In a traction elevator, a counterweight is used to balance the load of an elevator car, thus reducing power required for the vertical movement of the elevator car. The elevator car and the counterweight are attached to the opposing ends of a hoisting cable and they move reciprocally in the elevator shaft. The movement of the counterweight is usually directed by at least one guide rail, typically by two that are located on two opposing sides of the counterweight.
The counterweight is formed of a metal frame, often including two vertical side beams and two horizontal crossbeams. The weight of the counterweight is adjusted with filler pieces, balancing modules or counterweight modules that are packed within the frame. The counterweight further has an attachment mechanism for the hoisting cable and guide shoes mediating the contact between the counterweight and the guide rails.
The counterweight is placed in the elevator shaft and often space for it, both in vertical and horizontal directions, is limited. At the same time, the counterweight needs to have a sufficient weight in order to perform its balancing ballast function effectively.
Typically, the ballast effect of a counterweight is achieved by filling the metal frame with modules or pieces made of steel or concrete. In order to fit each individual module into the frame between the two side beams, the modules must be inserted at an angle in relation to the side beams and the crossbeams. This means that it is not possible to fill the entire vertical open space of the frame with full length modules. As the frame is filled upwards from the lower crossbeam situated at the bottom of the frame, at a certain point it is no longer possible to angle the modules in order to fit them between the side beams, as the upper crossbeam at the top of the frame prevents sufficient angling of the modules.
As the filling efficiency is thus reduced, unnecessary unfilled or open vertical space within the frame remains. This means that the frame must be made higher in order to fill it with enough of counterweight modules to provide sufficient ballast effect and balance to the elevator, and subsequently, the counterweight requires more space at the upper and lower parts of the elevator shaft.
Earlier, the aforementioned problem has been solved by arranging openings into the upper part of the vertical side beams of the frame, through which the remaining vertical open space may be filled by inserting modules while keeping them level with the crossbeams. The openings affect the structural integrity of the frame.
Alternatively, the remaining vertical open space of the frame may be filled with modules that are shorter than the vertical span between the two side beams, and thus fit between the two side beams in a level position. The shorter modules are then locked onto the frame with separate connectors. With this solution the mass distribution within the counterweight is not symmetric, which affects the balancing function of the counterweight.
Yet another solution is to construct bipartite modules from steel, which are form-locked together as they are inserted into the frame. These kinds of modules are expensive when made of steel, while constructing similar form-locking modules from concrete is very difficult, if not impossible.